David Weaver
gray slurry on top is from many uses. This stone makes an immediate black slurry if it's cleared and used with laminated tools. It'll make a black slurry with typical solid tool steel western tools, too. I leave the slurry on it because it's not really any better or finer without it (unlike a razor stone, it won't just work without generating a slurry indefinitely if used with light pressure) and there's no need to go to the effort of constantly clearing it off.

Inexpensive because it's oddly shaped - it's very wide, probably only about 6 1/2 to 7 inches long, and the strongest cutting-for-fineness suita I've used out of perhaps 40. So, it's the one I've kept (the other expensive white suita, I just haven't gone to the effort of selling yet as its price will make it a slow seller. This stone is actually a better day to day user at 1/8th the cost. Faster, tougher surface, pretty close in fineness).

I don't use middle and coarse natural japanese stones - they are not good stones and are soundly beaten by slurrying a novaculite stone instead for middle work. Of course, the revival of selling stones to westerners has brought the supply of those stones back (binsui, tanba aoto, iyo stones, etc) from $15 to sky is the limit price. Most pre-finishing stones of any quality are for swords and leave a coarser finish - pointless for tools, going back to novaculite. Most of the coarse japanese stones are just silica stones, they aren't as aggressive as novaculite, their natural particle variance can be really large, and they're slow.

But I guess some people do like to re-enact. I kept a couple at a time when I was pushing stones through etsy because someone will always want to learn for themselves rather than following advice of someone who has seen much more (the reason I've seen so much more than most is the same - I had to try it, too).

All that said, the smooth, tough surface and fast working smoothers like this stone are practical and pleasant. I'd use this one over any synthetic.